Intermolecular separation determines the extent of orbital overlap and thus the rate of electron transfer between neighbouring molecules in an organic crystal. If such a crystal is compressed, the resistivity decreases owing to a diminishing intermolecular distance1. Metal–insulator transitions have been observed by applying hydrostatic pressure to, for example, Langmuir films of metal nanoparticles2,3. But previous attempts to observe a clear transition point in organic crystals, such as anthracene and tetracene, were not successful owing to difficulties with electrically insulating the high-pressure cell4. Here we report a different approach by using a sample that is photoconductive and forms an organized film. A cylindrical tip (∼100 μm in diameter) was used to compress the sample instead of a piston/cylinder structure, entirely eliminating the problem of electrical insulation. Furthermore, by illuminating the sample with a laser, the conductivity of the sample is increased by several orders of magnitude. By monitoring the photocurrent with sensitivity at the 10-13 A level, changes in resistivity at very low pressure could be monitored. We observe a sharp increase in current that could indicate a transition from hopping to delocalized conduction.
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Drickamer, H. G. & Frank, C. W. Electronic structure, electronic transitions, and the high pressure chemistry and physics of solids. Annu. Rev. Phys. Chem. 23, 39–64 (1972)
Collier, C. P., Saykally, R. J., Shiang, J. J., Henrichs, S. E. & Heath, J. R. Reversible tuning of silver quantum dot monolayers through the metal-insulator transition. Science 277, 1978–1981 (1997)
Henrichs, S., Collier, C. P., Saykally, R. J., Shen, Y. R. & Heath, J. R. The dielectric function of silver nanoparticle Langmuir monolayers compressed through the metal insulator transition. J. Am. Chem. Soc. 122, 4077–4083 (2000)
Samara, G. A. & Drickamer, H. G. Effect of pressure on the resistance of fused-ring aromatic compounds. J. Chem. Phys. 37, 474–479 (1962)
Liu, C.-Y., Pan, H.-L., Tang, H., Fox, M. A. & Bard, A. J. Effect of structural order on the dark and photocurrents in zinc octakis (β-decoxyethyl)porphyrin thin-layer cells. J. Phys. Chem. 99, 7632–7636 (1995)
Schouten, P. G., Warman, J. M., de Haaas, M. P., Fox, M. A. & Pan, H-L. Charge migration in supramolecular stacks of peripherally substituted porphyrins. Nature 353, 736–737 (1991)
Liu, C.-Y. & Bard, A. J. Optoelectronic properties and memories based on organic single-crystal thin films. Acc. Chem. Res. 32, 235–245 (1999)
Liu, C.-Y. & Bard, A. J. in Conjugated Oligomers, Polymers, and Dendrimers: From Polyacetylene to DNA (ed. Brédas, J.-L.) 85–116 (De Boeck Université, Paris, 1999)
Gregg, B. A., Fox, M. A. & Bard, A. J. Photovoltaic effect in symmetrical cells of a liquid crystal porphyrin. J. Phys. Chem. 94, 1586–1598 (1990)
Liu, C.-Y. & Bard, A. J. Optoelectric charge trapping/detrapping in thin solid films of organic azo dyes: Application of scanning tunneling microscopic tip contact to photoconductive films for data storage. Chem. Mater. 10, 840–846 (1998)
Liu, C.-Y., Pan, H.-L., Fox, M. A. & Bard, A. J. Reversible charge trapping/detrapping in a photoconductive insulator of liquid crystal zinc porphyrin. Chem. Mater. 9, 1422–1429 (1997)
Aust, R. B., Bentley, W. H. & Drickamer, H. G. Behavior of fused-ring aromatic hydrocarbons at very high pressure. J. Chem. Phys. 41, 1856 (1964)
We thank F.-R.F. Fan for discussions. This work was supported by the National Science Foundation and the Robert A. Welch Foundation.
The authors declare that they have no competing financial interests.
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Liu, Cy., Bard, A. Pressure-induced insulator–conductor transition in a photoconducting organic liquid-crystal film. Nature 418, 162–164 (2002). https://doi.org/10.1038/nature00875
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